Modal and Stiffness Proportional Damping

OpenSees allows you to use both modal damping and stiffness proportional damping in a dynamic analysis. This combination of damping models is useful when you want to control damping in the low frequency modes and not let undamped high frequency response tarnish the analysis. Consider a simplified model of a 40 story building. The story … Continue reading Modal and Stiffness Proportional Damping

Eigenvalues of the Stiffness Matrix

Students are exposed to eigenvalues and eigenvectors a few times through their structural engineering education. After the math department's obligatory treatment to sophomores with definitions, characteristic polynomials, and toy matrices, two to three years pass before students see eigenanalysis again as first year graduate students: Structural dynamics - find natural modes of vibration of a … Continue reading Eigenvalues of the Stiffness Matrix

Two Thousand Concrete23!

Happy new year! Although the long-awaited Concrete23 will not be released this year, I look forward to what lies ahead with OpenSees. Being the first full week of January, it's blog delurking time. Long time listeners, first time callers, say hello in the comments section and let everyone know what you're OpenSeesing in 2023.

Eccentrically Loaded Bolt Groups

Tables 7-6 through 7-13 of the AISC Steel Manual contain values for C, the effective number of bolts that resist shear in eccentrically loaded bolt groups. For example, in a bolt group with three vertical rows of 4 bolts spaced s=3 inch with srow=3 inch row spacing and a load at $latex \theta$=30 degrees from … Continue reading Eccentrically Loaded Bolt Groups

Sometimes Tags Don’t Matter

When building a model in OpenSees, you have to ensure that you have unique tags for your domain components (nodes, elements, patterns, time series, parameters, etc.), reliability components (random variables, limit state functions, etc.), and model building components (materials, sections, beam integrations, etc.). If you define a duplicate tag, you will get an error message. … Continue reading Sometimes Tags Don’t Matter

A Simple Material Tester

A UniaxialMaterial tester was my first foray into Tk widgets back in the early 2000s. The tester has come along for the ride through all the OpenSees source code repositories. First cvs, then svn, and now GitHub. You could select various materials and drag the slider back and forth to see the stress-strain response history. … Continue reading A Simple Material Tester